The allies in central and southern Italy had fought side by side with Rome in several wars and had grown restive under Roman autocratic rule, wanting instead Roman citizenship and the privileges it conferred. In 91 bc the Roman tribune Marcus Livius Drusus tried to solve the problem by proposing legislation that would have admitted all Italians to citizenship, but his program aroused heated opposition in the Senate, and Drusus was soon afterward assassinated. The frustrated Italian allies then rose in revolt.

The peoples of the hills of central Italy formed the heart of the uprising, the Marsi in the north and the Samnites in the south. Neither the Latin colonies nor Etruria and Umbria joined in. The Italians began organizing their own confederacy; they established their headquarters at Corfinium, which they renamed Italia, created a Senate and officers, and issued a special coinage; soon they had 100,000 men in the field. In 90 bc Roman armies were defeated in the northern sector, while in the south the Italians were equally successful and burst into southern Campania. Only by political concession could Rome hope to check the revolt: the consul Lucius Julius Caesar thus helped pass a law granting Roman citizenship to all Italians who had not participated in the revolt and probably also to all who had but were ready to immediately lay down their arms. This move pacified many of the Italians, who soon lost interest in further struggle against Rome. Roman forces under Gnaeus Pompeius Strabo in the north and Lucius Cornelius Sulla in the south soon inflicted decisive defeats on the remaining rebels and captured their strongholds.

The back of the revolt was now broken, although some resistance continued among the Samnites for a short time. Further legislation was soon passed that reinforced the allies’ newly won rights; one law regulated the municipal organization of the communities that now entered the Roman state; and another dealt with Cisalpine Gaul (probably granting citizenship to all Latin colonies). Thus, the political unification of all Italy south of the Po River was achieved, and Romans and Italians, hitherto linked by alliance, could now become a single nation.